1. Field of the Invention
The present invention generally relates to a cutting torch and, more particularly, is concerned with an attachment for the cutting torch that facilitates cutting of circular holes with the torch.
2. Description of the Prior Art
Using a cutting torch freehand to cut accurate circles or circular arcs in metal plate is a very difficult task, even for an experienced welder. It is possible to inscribe the desired circle or arc on the metal plate before cutting. However, this approach still requires the welder to follow the inscribed circle or arc freehand thereby reducing accuracy and it also involves the extra step of inscribing the circle or arc on the metal plate.
A second and better approach utilizes an attachment which helps the welder guide the head of the cutting torch through the desired circular path. There are many attachments that are intended to guide the head of a cutting torch in an accurate circular path. Common to many of these attachments is a center pin and means which fix the center pin to the cutting torch at a distance from the head of the cutting torch equal to the radius of the desired circle or arc. The center pin is placed in a centerpunch mark located at the center of the desired circle or arc and the head of the torch is rotated about the center pin to cut an accurate circle or arc. There is no need to inscribe the circle or arc onto the metal plate. Only the center of the circle need be located and punched.
Most attachments utilize a variety of center pins including straight center pins and offset center pins to provide them with the capability of cutting circles with a wide range of radii. The primary difference between many of the available attachments is the means by which the center pin is fixed on the cutting torch. The simplest and least cumbersome attachments fix the center pin to a single clamping member that clamps onto the tubes that extend between the handle portion and the head portion of the cutting torch. Examples of such attachments are disclosed in U.S. Pat. No. 1,359,155 to Davis, U.S. Pat. No. 1,564,636 to Smith, U.S. Pat. No. 1,792,317 to Marsh and U.S. Pat. No. 2,743,101 to Clark and in Australian Pat. No. 223,932 to Steenbergen. These attachments are well adapted for attaching to the most common cutting torches having two tubes aligned in the same vertical plane. However, some cutting torches have three tubes arranged in a triangular configuration, with either a single upper tube and two lower tubes or two upper tubes and a single lower tube. Because of the nature of the clamping members employed by each of these attachments, they cannot be conveniently attached to cutting torches having tubes arranged in a triangular configuration.
Because cutting a straight line freehand with a cutting torch is also very difficult, an attachment which helps guide the cutting torch in a straight line is often useful. Since a single cutting torch may alternatively be used in making circular cuts and straight cuts, it is desirable if one attachment is capable of accomplishing both tasks with a minimum of adjustments.
Consequently, a need still exists for an attachment for a cutting torch that may clamp onto the tubes of the cutting torch regardless of whether the tubes are aligned in the same vertical plane or are arranged in a triangular configuration and may easily be adapted for making both circular cuts and straight cuts.